| Popis: |
During the end fitting (EF) assembly, the tensile armors of flexible pipes are folded and then unfolded to allow the assessment to the inner sheath and the activation of the inner sealing system. This procedure leaves residual stresses and plastic deformations on these armors, which affect their fatigue resistance and, consequently, the overall performance of the pipe. Hence, in this work, a methodology to predict the fatigue resistance of tensile armors inside an EF is proposed. This methodology relies on stresses calculated with a previously presented three-dimensional finite element (FE) approach and is employed to analyze the fatigue response of a 6” production riser in catenary configuration. This fatigue analysis not only addresses the effects from several irregular sea states but also the local stress concentrations associated with the EF assembly and pre-operational tests (e. g., Factory Acceptance Test, FAT). The results obtained indicate that the EF entrance may be a critical point for fatigue failure and, moreover, the lower fatigue resistance is related to a region where higher alternate stresses occur despite the very high mean stresses are observed in other regions along the tensile armors. |
